The first sunitinib (total drug) pharmacokinetics day will be performed after steady-state sunitinib levels are reached, meaning at least 14 days after starting sunitinib 25 - 50 mg per day treatment (week 3 in the treatment cycle of sunitinib). On this first pharmacokinetic day a dose of midazolam 7.5 mg will be given at the same time as the sunitinib dose, to observe the effect of sunitinib on CYP3A4 capacity. Before the second pharmacokinetic day (day 28 of sunitinib treatment) the patient will drink 3 times a day a glass of grapefruit juice or orange juice for three consecutive day.Patients will be assigned either to a grapefruit juice or orange juice arm. On this second pharmacokinetic day the patient again will use a dose of midazolam at the sam time as the sunitinib dose, to observe the effect of grapefruit juice or orange juice on the metabolic capacity pf CYP3A4. The third pharmacokinetic day will take place at the end of week 6 of the treatment cycle, the second week of the 2 week off period. The patient will receive a single oral dose of midazolam 7.5mg, followed by midazolam pharmacokinetics to determine the base-line CYP3A phenotypic expression. Pharmacokinetic parameters based on measurement in plasma samples will be compared between the treatment periods.